Archive for October, 2010

VoIP is often the first service people think of when QoS is mentioned, although most of the early deployments made do without QoS at all. For the enterprise, VoIP was either restricted to LANs with plentiful bandwidth so that contention issues were rare, or, if allowed out into the WAN, given a separate connection to keep it safe from other traffic. Conversely VoIP was – and still is – extensively used to bypass international telco transit charges, with contention carefully avoided by means of dynamic macro-level routing.

So does VoIP really need QoS? To move into the mainstream and deliver on its promise of low-cost and ubiquitous communications, VoIP must co-exist with other applications. As the supporting VoIP infrastructure matures, the cost of protecting VoIP traffic by over-allocating bandwidth starts to become a serious issue. A VoIP call typically consumes only 100k or so, but without effective QoS it needs much more bandwidth allocated than this to reduce the impact that contention with other traffic has on the loss and delay of the VoIP packets. On a DSL or wireless connection wasting so much bandwidth can be prohibitive. In any case, ensuring that this bandwidth is reserved when other applications are greedily trying to use it requires a basic form of QoS! Using more powerful QoS that can deliver the loss and, particularly, latency bounds that VoIP requires without over-allocation makes a far more efficient use of network resources.

How low the loss and latency must be kept for VoIP packets are across any particular network link depends on two things: how much the VoIP application can tolerate overall (its “budget”); and how much is introduced by the rest of the end-to-end network path. The tolerance of VoIP to loss and latency has improved over time with better codecs and clever jitter and loss concealment techniques, but delay in particular is ultimately constrained by human factors (think of the old intercontinental phone calls that went via satellite!). In the overall mouth-to-ear path a lot of time is taken by the process of sampling and serializing sound, and the speed of light is also a factor, particularly when complex network architectures may make the packet path less than direct!

As video traffic expands to fill every bandwidth upgrade, the days when VoIP could expect to traverse the network unscathed recede ever further into the past. Without effective QoS to allow VoIP to coexist with video and the other traffic, the days when it seemed a good way to talk will recede into the past as well.

We wrote about Net Neutrality in a previous post, but this is a big topic worthy of further discussion. Part of the heat in the debate comes from an identification of “equal treatment of all packets” with “equal opportunity for all providers”. The assumption is that a uniform best-effort service empowers “the little guy” to compete with industry titans, and so encourages innovation. On the other hand, a draconian interpretation of “neutrality” discourages innovation by network service providers, which isn’t in the best interests of end users either.

Is there a way out of this impasse? Well, let’s think about a situation in which the NSP offers a differentiated service to end users in which it’s up to the users to decide what they do with it. Suppose a user pays for a service from ABC Telco where 100kbps of their bandwidth is guaranteed to have low latency (or at least lower latency than the rest). They could then subscribe to a VoIP service provider, who sends packets to them with an appropriate priority marking. ABC Telco delivers them with priority treatment, provided their bandwidth doesn’t exceed 100kbps (if it does, ABC discards the excess; this discourages abuse of the service). The user can switch NSP and VSP independently, and choose large or small providers without prejudice.

This may not be the only way to solve the problem, but it shows that it needn’t be insoluble if we have a rational debate about what kind of “neutrality” or “fairness” we actually want. Undifferentiated best effort service means being equally unfair to everybody, and it’s time we started doing better: giving packet streams differential treatment has the potential to spur a new wave of services that wouldn’t work well over best effort.

Recent announcements have highlighted the increasing importance of policy as a tool for controlling access to network resources and for developing differentiated service offers. O2 is to offer different packages based on controlled access to streamed content – the more you pay, the more concurrent sessions you can run (see “O2 tightens up traffic management policy“. When considered with the recent news from Demon regarding special packages for gamers (see “Demon UK to offer priority service for gamers” for more details), it’s clear that service providers recognise a growing need to cater for different kinds of users and applications in consumer markets.

But, the really interesting perspective is the potential this creates for service providers to identify new revenue streams and to leverage their network assets. Instead of just offering packages based on usage and bandwidth, service providers can create further differentiation by launching offers that cater for specific needs and applications that are actually being used by customers. With so many different types of traffic, the ability to recognise particular streams and to apply an appropriate policy (or, in effect, class of service) will become increasingly valuable and represents an opportunity for service providers to generate additional revenue by doing something they have to do anyway – optimise their networks.

The implementation of policies, reinforced by predictable, flexible QoS mechanisms will be critical to ensuring future profitability. It’s apparent that the industry is starting to recognise this and we anticipate a flurry of similar announcements in the coming months. All you can eat may still be an option, but it’s one that may attract premium pricing. Anything less than all you can eat will be likely be priced accordingly.